1. Field of the Invention
The present invention relates to a longitudinal profile measuring apparatus for measuring longitudinal profiles of roads, airports, rails, tunnels or the like, and more specifically, to a longitudinal profile measuring apparatus which is capable of accommodating specified evaluating techniques.
2. Description of the Related Art
Longitudinal profile measuring apparatuses which have been conventionally used are of two types. One is called a wheel type in which the apparatus has a relative distance meter located in a center of a frame supported by a plurality of wheels and is moved along a measuring line manually to measure a moving distance and a relative distance to a target surface. A graph is output on which the abscissa represents moving distance and the ordinate represents relative distance for showing a rough profile. The other apparatus is called a reaction or an inertial type in which a vehicle, provided with a relative distance meter, an acceleration meter and a moving distance meter, travels on the target surface to measure the rough profile from both outputs of the relative distance meter and acceleration meter.
When a road is measured as a target surface, for example, evaluation of the roughness of its longitudinal profile is used as an evaluation of road quality. This is used to determine the need for road repair or as an evaluation of the quality of road construction and is a useful technique in the industry.
In order to unify the evaluation, for example, an International Roughness Index (IRI) has been developed and proposed in association with investments by the World Bank. In order to calculate the IRI, it is necessary to measure a rough profile of a road surface by means of an apparatus having gain with a specified frequency characteristic. The specified frequency characteristic is artificially determined based on riding comfort of a car which is called xe2x80x9ca golden carxe2x80x9d.
However, in a conventional longitudinal profile measuring apparatus of the wheel type, the frequency characteristic has a roughness which is determined depending upon a physical space between the wheels. This causes a problem in that the specified frequency characteristic such as the IRI cannot be accommodated.
Further, while a sub-frame can be added to increase multiplicity for making the frequency characteristic even, this requires the use of more wheels and a complex structure.
Further, finding the IRI requires information on a gradient, however, in the conventional longitudinal profile measuring apparatus of a wheel type, a relative distance to a target surface is obtained directly. Thus, there is a problem that detecting sensitivity to a short wavelength with low roughness is reduced even for the same gradient.
On the other hand, in the reaction or inertial type of longitudinal profile measuring apparatus, measurement should be carried out in a certain high-speed condition. This requirement causes a problem in that measurement is impossible in a low-speed condition or when stopping at a signal or the like. Thus, it becomes difficult to measure a short distance and requires correction at a curve or the like.
Also, a problem is that the apparatus requires a sensor with high accuracy, which results in a higher price.
In view of the foregoing and other problems, disadvantages, and drawbacks of the conventional longitudinal profile measuring apparatuses, the present invention has been devised, and has as its object the provision of a longitudinal profile measuring apparatus which can be configured at a low price and is provided with a desired frequency characteristic.
In order to attain the object suggested above, and to solve the above problems, a longitudinal profile measuring apparatus according to the present invention includes a frame supported by more than two wheels in a row in a direction of a measuring line, a relative distance meter located on the frame for measuring relative distance to a target surface, a moving distance meter for measuring moving distance of movement along the measuring line on the target surface, and data processing means for finding spatial data, which show a rough profile of the target surface, along the measuring line from the relative distances measured by the relative distance meter.
The data processing means includes storing means for storing relative distance data to the target surface measured by the relative distance meter associated with moving distance data measured by the moving distance meter when moving along the measuring line, frequency transforming means for transforming the relative distance data of the data stored by the storing means into amplitude corresponding to frequency, correction coefficient multiplying means for multiplying the amplitude corresponding to frequency by coefficient of correction for allowing the apparatus to have a gain with a desired frequency characteristic, and inverse frequency transforming means for inverse transforming the corrected amplitude to find the corrected spatial data of the target surface.
A longitudinal profile can be captured in the form of gathered relative distance data to the target surface per predetermined distance from a base point measured by the relative distance meter. The data includes a roughness with small variation and a roughness with large variation. Taking notice of such cycle variation, Fourier transform by the frequency transforming means allows the data to be transformed into the amplitude corresponding to frequency. In the Fourier transform, the spatial data on which the abscissa represents the moving distance and the ordinate represents relative distance and frequency amplitude data on which the abscissa represents the frequency and the ordinate represents components of sine and cosine can be mutually transformed. By means of the Fourier transform, a spatial function f(x) of the cycle L is developed into an orthogonal function series of sin(xcfx89nX) and cos(xcfx89nX) with each frequency xcfx89n=2nxcfx80/L as the following equation:                               F          ⁡                      (                          jω              n                        )                          =                              ∫                                          -                L                            /              2                                      L              /              2                                ⁢                                    f              ⁡                              (                x                )                                      ⁢                          ⅇ                                                -                  j                                ⁢                                  xe2x80x83                                ⁢                                  ω                  n                                ⁢                x                                      ⁢                          xe2x80x83                        ⁢                          ⅆ              x                                                          (        1        )            
Amplitudes of sin(xcfx89nX) and cos(xcfx89nX) are respectively represented in imaginary and real parts of the equation (1).
A function of the frequency F(jxcfx89n) is inverse Fourier transformed by the following equation by the inverse frequency transforming means to be returned to the function of the space f(x).                               f          ⁡                      (            x            )                          =                              1            L                    ·                                    ∑                              n                =                                  -                  ∞                                            ∞                        ⁢                                          F                ⁡                                  (                                      j                    ⁢                                          xe2x80x83                                        ⁢                                          ω                      n                                                        )                                            ⁢                              ⅇ                                  j                  ⁢                                      xe2x80x83                                    ⁢                                      ω                    n                                    ⁢                  x                                                                                        (        2        )            
Now, considering the apparatus shown in FIG. 1, having the frame 10 supported at both its ends by the wheels 12A, 12B and having the relative distance meter 18 located on its center, as shown in FIG. 3, measuring gain of the apparatus has a frequency characteristic as described below when a space between each of the wheels 12A, 12B and the relative distance meter 18 is xe2x80x9caxe2x80x9d.
Namely, when the apparatus moves on a triangular wave ejxcfx89nx of angular frequency xcfx89n as shown in FIG. 3, output fxcfx89n(X) of the relative distance meter can be represented by the following equation:                                                                         f                ⁢                                  xe2x80x83                                ⁢                                                      ω                    n                                    ⁡                                      (                    x                    )                                                              =                              C                -                                  (                                                            y                      2                                        -                                                                  (                                                                              y                            1                                                    +                                                      y                            3                                                                          )                                            2                                                        )                                                                                                        =                              C                -                                  ⅇ                                      j                    ⁢                                          xe2x80x83                                        ⁢                                          ω                      n                                        ⁢                    x                                                  +                                                      (                                                                  ⅇ                                                  j                          ⁢                                                      xe2x80x83                                                    ⁢                                                                                    ω                              n                                                        ⁡                                                          (                                                              x                                -                                a                                                            )                                                                                                                          +                                              ⅇ                                                  j                          ⁢                                                      xe2x80x83                                                    ⁢                                                                                    ω                              n                                                        ⁡                                                          (                                                              x                                +                                a                                                            )                                                                                                                                            )                                    2                                                                                                        =                              C                -                                                      (                                          1                      -                                              cos                        ⁡                                                  (                                                                                    ω                              n                                                        ⁢                            a                                                    )                                                                                      )                                    ·                                      ⅇ                                          j                      ⁢                                              xe2x80x83                                            ⁢                                              ω                        n                                            ⁢                      x                                                                                                                              (        3        )            
where C represents mounting distance of a sensor and is constant.
Accordingly, the measuring gain G is as follows:
G=1xe2x88x92cos(xcfx89na)xe2x80x83xe2x80x83(4)
Here, when a wavelength is xcex, xcfx89=2xcfx80/xcex to be as follows:
G=1xe2x88x92cos(2xcfx80a/xcex)xe2x80x83xe2x80x83(5)
The gain is determined by a ratio of a/xcex as shown in FIG. 4. As clarified in the figure, the inherent frequency characteristic of the gain specific to the apparatus is as follows:
When xcex=2a/(2N+1), G=1xe2x88x92cos((2N+1)xcfx80)=2, which is maximum
When xcex=a/N, G=1xe2x88x92cos(2xcfx80N)=0, which is minimum
where N represents integer.
The inherent frequency characteristic specific to this apparatus is obtained in advance by calculation or experiment. And, thereafter there is obtained the coefficient of correction so that this frequency characteristic will become any desired frequency characteristic. For example, when the apparatus is desired to have a certain constant frequency characteristic, as shown in FIG. 5, the coefficient of correction is made as shown by a continuous line against the original frequency characteristic of the gain shown by a dashed line for allowing the multiplied result to have a certain constant gain.
An influence of the frequency can be eliminated by measuring an optional longitudinal surface, finding the amplitude corresponding to frequency by the Fourier transform by the frequency transforming means, multiplying the amplitude by the coefficient of correction by the correction coefficient multiplying means and then returning the result to the longitudinal surface by the inverse Fourier transform by the inverse frequency transforming means.
When finding an IRI, the coefficient of correction is determined in advance such that a result of multiplying the coefficient of correction has an IRI characteristic as shown in FIG. 6, and after Fourier transformed and multiplied by the coefficient of correction, the data is inverse transformed into the spatial data and the IRI can be found by accumulating variations of gradient based on the spatial data.
Conventionally, the IRI has been found by accumulating variations of gradient detected by a measurement prototype called the golden car, which theoretically follows a vehicle dynamic model. The vehicle dynamic model of the golden car is defined by a spring modulus of tires, a spring modulus of axles, or weights of tires and axles, and has a different phase characteristic from that of this apparatus as well as the frequency characteristic. However a difference relative to the same wavelength between the golden car and this apparatus is constant. Thus by subtracting the difference from a phase as originally measured by this apparatus, an output waveform can be transferred so as to be a similar waveform obtained by the golden car. Alternatively, such a subtracting can be performed so that an output waveform can be transferred so as to reproduce a real longitudinal profile.
The coefficient of correction for a gain with a desired frequency characteristic and the difference of phase between a desired phase characteristic and an inherent phase characteristic can be found by simulation calculations. In the simulation calculations, frequency and phase characteristics of a simulation model of the apparatus responding to a step response are simulated and the simulated response is transformed by the Fourier transform to get a simulated frequency characteristic and a simulated phase characteristic. The coefficient of correction for a gain is then calculated by dividing a value at a certain frequency on the desired frequency characteristic by a value at the same frequency on the simulated frequency characteristic. The difference for phase is then calculated by subtracting a value at a certain frequency on the simulated phase characteristic from a value at the same frequency on the desired phase characteristic.
Besides the IRI, the apparatus can, of course, have an optional desired frequency characteristic such as to accommodate indexes other than the IRI, for example, a ride number (RN).
As shown in a part C of FIG. 5, when the gain becomes zero or close to zero, the coefficient of correction becomes large, leading to low accuracy. Thus, to have the desired frequency characteristic, it is desirable to reduce the roughness of the gain in a frequency band to be measured.
Therefore, by setting the spaces between the plurality of wheels and the relative distance meter to not be identical (e.g., to have different dimensions), the frequency characteristic of the gain can be made evener than a case where the spaces between the wheels and relative distance meter have the identical dimension (=a), as shown in FIG. 3. This is considered due to the influence of the various frequencies which are determined depending upon the different dimensions being mutually added. In the conventional measuring apparatus of wheel type, providing a single or multiple sub-frames makes the frequency characteristic of the gain evener and this effect tends to be larger for an increased number of multiple sub-frames. However, in the present invention, the frequency characteristic can be made even by a simple configuration without using the sub-frame. In the present invention, using the sub-frame in the simple configuration increases the effect.
The different dimensions of the spaces preferably have a ratio greater than 1:1.5 in case of internal division, and even more preferably greater than 1:2. In the case of the other ratio, external division is preferably taken. In the external division, the ratio is negative such as xe2x88x921:3 and preferably more than xe2x88x921:1.
FIG. 7(a) shows an example of a ratio of xe2x88x921:9 when externally divided such that the space between the relative distance meter 18 and one wheel 12A is xe2x80x9caxe2x80x9d and the space between the relative distance meter 18 and the other wheel 12B is xe2x80x9c9axe2x80x9d, and FIG. 7(b) shows a frequency characteristic in this case. Such a large ratio makes the frequency band more even in comparison with the case shown in FIG. 4.
Further, when evaluation of the roughness of the longitudinal profile in terms of the gradient is necessary (e.g., like IRI), making the spaces between the plurality of wheels and the relative distance meter respectively different in dimension can increase detecting sensitivity to a short wavelength.
FIG. 8 is an explanatory view of this concept where the abscissa represents moving distance and the ordinate represents relative distance in each of two graphs. FIG. 8(a) shows a longitudinal profile with high roughness and FIG. 8(b) shows a longitudinal profile with low roughness. These two longitudinal profiles have a different roughness but a same gradient, and FIG. 8(a) has a long wavelength and FIG. 8(b) has a short wavelength.
An apparatus, such as that of the present invention, for measuring the relative distance to the target surface, generally has a problem that the detecting sensitivity to the short wavelength with the low roughness as FIG. 8(b) is reduced. However, by making the spaces between the wheels and relative distance meter respectively different in dimension, the data measured by the action of the wheel with the short space to the relative distance meter have a large influence on the measurement value, and the data measured by the action of the wheel with the long space to the relative distance meter have a little influence on the measurement value.
The data measured by the action of the wheel with the short space to the relative distance meter strongly reflects a short wavelength component and the data measured by the action of the wheel with the long space to the relative distance meter strongly reflects a long wavelength component. This results in a reflecting of the short wavelength component more strongly to increase the detection sensitivity. Accordingly, it is advantageous in the evaluation manner as the IRI for evaluating the roughness using the gradient.
Optionally, instead of using the above described frequency transforming means, correction coefficient multiplying means, and inverse frequency transforming means, a space between one wheel and the relative distance meter is set to be about xc2xd of a longer wavelength in the frequency band to be measured of the longitudinal profile. Further, a space between the other wheel and the relative distance meter is set to be about xc2xd of a shorter wavelength in the frequency band to be measured of the longitudinal profile.
This length may be taken by either internal or external division, namely, the position of the relative distance meter may be inside or outside between one wheel and the other wheel. According to this approach, superposed effects of the long wavelength component, measured by the action of the wheel with the long space to the relative distance meter, and the short wavelength component, measured by the action of the wheel with the short space to the relative distance meter, can be obtained. Thus, the even frequency characteristic can be obtained between the longer wavelength and shorter wavelength.
Of course, it is also possible to combine the configuration in which the wheels and relative distance meter are set with the above spaces with the frequency transforming means, correction coefficient multiplying means and inverse frequency transforming means to obtain a frequency characteristic closer to the desired frequency characteristic. As the inherent frequency characteristic specific to the apparatus becomes more even, the burden (e.g., effect) of the correction of the correction coefficient multiplying means can be reduced to achieve a measurement with higher accuracy.
The wheels described above have a function of physically supporting the frame and a function of holding it a certain distance from the measuring surface. Thus, it is possible to use relative distance meters located on a vehicle instead of on the wheels and to regard output of the relative distance meters substituted for the wheels as a criterion.
Specifically, such a longitudinal profile measuring apparatus includes a plurality of relative distance meters located in a row in a direction of a measuring line on the vehicle for respectively measuring relative distance to a target surface, a moving distance meter located on the vehicle for measuring moving distance of movement along the measuring line on the target surface, and data processing means for finding spatial data, which show a rough profile of the target surface along the measuring line from the relative distance measured by the relative distance meter.
The data processing means includes storing means for storing relative distance data to the target surface measured by the plurality of relative distance meters associated with moving distance data measured by the moving distance meter when moving along the measuring line, and relative distance calculating means for calculating relative distances to be outputted by a main relative distance meter from the relative distance data measured by each relative distance meter.
The main relative distance meter is assumed to be substituted for one of the relative distance meters on the same vertical line as the main relative distance meter and to be supporting a phantom frame supported by phantom wheels which are assumed to be substituted for the other relative distance meters.
In this manner, spatial data is found based on the relative distance from the relative distance calculating means. Further, the plurality of relative distance meters are set so that spaces between the main relative distance meter and the other relative distance meters are such that the apparatus has a gain with a desired frequency characteristic.
Thus, by substituting the other relative distance meters for the wheels which have the function of holding a frame a certain distance from the measuring surface, it is possible to set spaces between the main relative distance meter and the other relative distance with increased freedom.
It is also possible that the apparatus having the plurality of relative distance meters instead of the wheels is combined with the frequency transforming means, correction coefficient multiplying means and inverse frequency transforming means to obtain the frequency characteristic closer to the desired frequency characteristic.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-161246, filed on May 30, 2000, and which is expressly incorporated herein by reference in its entirety.